1. Overview of the 3 DOF Parallel-Architecture Wrist Mechanism
Stephen Canfield, Professor
Department of Mechanical Engineering
Tennessee Technological University
November 10, 2008

2. Overview

3. About Parallel Mechanisms
Multiple load-bearing chains b/n output and base
Kinematics
Advantages
Stronger, lighter
Disadvantages
Reduced range of motion, kinematics

4. About the PAW 3-5R Spatial Parallel-architecture mechanism 3dof
Pitch, yaw, plunge

5. Characteristics of the PAW
High payload-to-weight, good dynamic performance
Ground-relative actuation
All-revolute design
Closed-form forward/inverse kinematics exist
Large range of motion in orientation
Singularity free workspace (interior),greater than hemisphere
Removes constraint on control algorithms
Improved dexterity

6. Advantages of proposed design
Parallel-architecture: High payload, accuracy, good dynamic performance in light-weight system
Large, singularity-free range of motion
Eliminate need for slip-rings
Provide accuracy needed for solar concentrators
Inherently redundant system
- Application for pointing solar arrays – Video

7. Gimbal Kinematics, Options

8. Past applications
Robotic end-effector, compliant design for pointing mirrors, sub 10nm precision manipulator

9. Point Design Applications: Thruster

10. Part Layout

11. Thruster as built

12. Application for pointing thruster

13. Design Point: Solar-Array Mount

14. Solary Array Mount

15. Table I: Summary of 3D solar-array tracking mechanism
Solar Array Mount
Component
Description
Mass/ Workspace
Motor Drive:
Maxon EC90 Flat Motor
1.5 lb
Drive reduction
Harmonic Drive HDC 1M
2.6 lb
Bearings
Bronze bushings, ¾, 3/8 ID
Shaft
440c SS
Link components
7075 Al
Mechanism weight *
(without actuation)
14.75 lb
3D Mechanism weight
(with actuation, includes a 20% factor)
32.5 lb
Working Volume*
5.5 inch radius cylinder
Height is selectable
5.5 inch cylinder
Stowed Volume*
3 high x 7 radius cylinder (inches)
7x3 inch cylinder
Table I: Summary of 3D solar-array tracking mechanism

16. Miniature Gimbal:

19. Compliant mechanism applications
High precision compact design
From known topology
Conventional 3 dof manipulator (pointing task)
Compliant 3 dof manipulator
Compact, 6 dof compliant manipulator

20. Kinematics

21. Force Analysis Closed-form kinetostatic analysis Beta=30 degrees

22. Path planning and trajectory control

23. Embedded electronics Currently Motorola S-12 family MCU
IK ~ 12k in HCS-12 CPU assembly (unoptimized)
8 channel PWM, Quadrature encoders, drivers

24. Summary